Turntable incorporating heating means and oven incorporating the same

ABSTRACT

A turntable ( 19 ) for an oven comprising a surface for heating a food item ( 27, 75 ) placed on the turntable ( 19 ), wherein the turntable ( 19 ) is provided with integral heating means ( 29 ). The turntable may be incorporated into an oven cavity ( 17, 67 ) of an oven.

This invention relates to an oven incorporating a turntableincorporating heating means.

Ovens, such as microwave ovens and fan-assisted ovens, generally haveone or more main heating means at the top or in an upper region of anoven cavity. Nevertheless, it is known to incorporate an auxiliaryheating means in the region of the base of the oven cavity. Such anauxiliary heating means is generally employed because current rapid cookovens, such as microwave ovens and top-grill ovens, cook the top andupper region of a food item placed in the oven cavity more effectivelythan the bottom or lower region thereof.

It has been proposed to arrange an auxiliary heating means beneath thelower wall of the oven cavity of a microwave oven, but such anarrangement has the disadvantage that it is necessary first to heat thebase of the oven cavity and then to rely on convection and conductionfrom the base to the food item being cooked. In cases where the oven isprovided with a turntable, the turntable forms a further barrier to thetransfer of heat to the food item being cooked.

It has also been proposed to provide an auxiliary heating means withinthe oven cavity of a microwave oven. Such an arrangement is known, forexample, from U.S. Pat. No. 3,172,987 and U.S. Pat. No. 4,326,113.According to U.S. Pat. No. 3,172,987 a sheathed resistance heatingelement is mounted slightly above the base of an oven cavity beneath aturntable. A similar arrangement is shown in U.S. Pat. No. 4,326,113except that the sheathed heating element substantially protrudes beyondthe periphery of the turntable. The arrangement of a sheathed heatingelement within the oven cavity has the disadvantage that the heatingelement is relatively exposed and readily becomes soiled, while beingrelatively difficult to clean.

It has further been proposed in U.S. Pat. No. 4,132,216 to provide ahot-air oven for heating food-loaded cartridges which are arranged in anannular array on a turntable. Air is heated at the top of the ovencavity and blown by a propeller into the hollow core formed by theannular array, such that part of the air passes through holes in thecartridges and past food containers therein, while the remainder of theair passes through a flow passage beneath the cartridges and above theturntable. The arrangement of a heating element and a propeller withinthe oven cavity gives rise to the disadvantage that the internalcomponents are difficult to clean, while the propellor is potentiallydangerous and requires to be shielded from the user.

It is therefore an object of the present invention to provide an ovenwhich overcomes or ameliorates the above disadvantages.

According to the present invention there is provided an oven comprisingan oven cavity, a main heating means for heating a food item, and aturntable arranged in a lower region of the oven cavity and comprising asurface for heating a food item placed on the turntable, wherein theturntable is provided with integral electrical heating means and withelectrically-conductive means for connecting the integral electricalheating means to a source of electrical power.

The heating means may comprise an elongate electrically conductingmaterial embedded into the turntable, for example into a lower surfacethereof.

Alternatively, the heating means may comprise a thick film heatingelement, for example applied to an underside and/or an upper surface ofthe turntable.

As a further alternative, the heating means may comprise a heatingelement wrapped around an insulating board, such as of mica.

The turntable may include a layer of thermal insulation material on alower surface thereof.

According to another alternative, the heating means may comprise aheating element provided within a dish-like support containing a baselayer of thermal insulation material. The base layer may comprisemicroporous thermal and electrical insulation material. The heatingelement may be supported relative to the base layer.

The heating element may comprise a corrugated metal ribbon mountededgewise on the base layer and secured by partial embedding and/or acoiled wire or coiled ribbon secured to the base layer and/or a lampmounted above the base layer and/or a sheathed heating element and/or aresistance element mounted within a glass tube.

A peripheral wall of thermal insulation material may extend around theinternal periphery of the dish-like support.

The heating power output of the heating means may increase withincreasing distance from an axis of rotation of the turntable.

The turntable may include conductive tracks connected to the heatingmeans for supplying power to the heating means. The conductive tracksmay be in the form of annular tracks provided on an underside of theturntable and/or may be provided around the periphery of a support shaftprovided on an underside of the turntable.

The main heating means may comprise a magnetron or a resistance heatingelement and fan means for propelling air past the heating element andinto the oven cavity. The main heating means may further comprise agrill element for directing radiation downwardly towards the food item.

For a better understanding of the present invention and to show moreclearly how it may be carried into effect reference will now be made, byway of example, to the accompanying drawings in which:

FIG. 1 is a plan view of an embodiment of a microwave oven provided witha turntable incorporating heating means according to the presentinvention, the top of the oven being omitted for clarity;

FIG. 2 is a front elevational view of the microwave oven shown in FIG. 1with the door removed for clarity;

FIG. 3 shows on a larger scale one embodiment of a turntable for usewith the microwave oven of FIGS. 1 and 2;

FIGS. 4 and 5 show one way in which the heating means of the turntableof FIG. 3 can be connected to a supply of electricity;

FIGS. 6 and 7 show another embodiment of a turntable for use with themicrowave oven of FIGS. 1 and 2;

FIG. 8 is a plan view of an embodiment of a fan-assisted oven providedwith a turntable incorporating heating means according to the presentinvention, the top of the oven being removed for clarity; and

FIG. 9 is a front elevational view of the fan-assisted oven of FIG. 8with the door removed for clarity.

The microwave oven shown in FIGS. 1 and 2 comprises a body having a top1, a base 3, a back 5, side walls 7 and 9 and a door 11 provided with ahandle 13 for opening and closing the door. A control panel 15 isprovided for controlling operation of the oven. Provided within an ovencavity 17 is a turntable 19 which is rotatable in known manner when theoven is in operation. A plurality of feet 21 are provided beneath theoven body to support the oven on a suitable surface (not shown).

A magnetron, shown diagrammatically at 23, is provided in a chamberbehind the control panel 15 and functions as a main heating means tosupply microwaves in known manner into an upper region of the ovencavity 17 as indicated by arrows 25. The microwaves are very effectivein heating the upper part of a food item 27, but are not as effective inheating the lower part of the food item.

The upper part of food item 27 may additionally be heated with a grillheater (not shown) provided in the top 1 of the oven body and directeddownwardly onto the upper part of the food item.

However, while the magnetron and a grill if provided effectively heatthe upper part of the food item, the lower part of the food item is noteffectively heated and this can lead either to the upper part of thefood item being over-cooked or the lower part of the food item beingunder-cooked. Either case is visually undesirable, while under-cookingof the lower part of the food item can be hazardous to health.

According to the present invention there is integrated into the base ofthe turntable 19 an auxiliary heater 29. The auxiliary heater 29 is notrequired to provide heat to the entire oven cavity, only to the lowerregion of food item 27. Thus the power output of the auxiliary heatercan be relatively low, for example 200 watts.

One embodiment of the auxiliary heater 29 shown in FIGS. 1 and 2 isillustrated in more detail in FIG. 3 and comprises an elongate strip ofelectrically conducting material embedded into the lower surface of theturntable. Alternatively, the auxiliary heater may comprise a thick filmheater applied to the lower or upper surface of the turntable, or aheating element wrapped around an insulating board, such as of mica, andarranged at a lower surface of the turntable. If desired a layer ofthermal and/or electrical insulation material 31 may be provided on thelower face of the turntable 29. Because the heat output of the auxiliaryheater 29 is relatively low, the material of the turntable need not havehigh-temperature-resistant properties and may be, for example, arelatively low-temperature glass such as borosilicate glass, for examplethat sold under the trade mark Pyrex.

Electrical power to the auxiliary heater may be provided in a number ofways. For example, as shown in FIG. 4, which shows part only of theturntable 19, brushes or spring-biased contacts 33 may be provided inthe base of the oven cavity and may contact annularelectrically-conductive tracks 35 provided on the underside of theturntable 19. If required, the brushes or contacts 19 may be providedwith means (not shown) for cutting electrical power thereto in the eventthe turntable 19 is removed from the oven cavity.

Alternatively, as shown in FIG. 5, which also shows part only of theturntable 19, electrical power for the auxiliary heater 29 may beprovided by slip ring connectors in the form of peripheralelectrically-conductive tracks 37 may be provided on a rotatable shaft41 on which the turntable is supported, which tracks may be contacted bybrushes or spring-biased contacts 39.

FIGS. 6 and 7 show an alternative form of construction of turntableincorporating an auxiliary heater 29, FIG. 6 employing the slip ringconnectors of FIG. 5 and FIG. 7 employing the electrically-conductivetracks of FIG. 4 provided on the lower surface of the auxiliary heater.

The turntable 19 shown in FIGS. 6 and 7 comprises an upper, slightlydished member 43, for example of glass, glass ceramic or other suitablematerial and an auxiliary heater 29 mounted beneath the dished memberand secured thereto. The heater 29 is rotatably mounted on a shaft 41 soas to be spaced above the base 3 of the oven.

The auxiliary heater 29 comprises a dish-like support 45, for example ofmetal or other suitable material, provided with a base layer 47 ofthermal insulation material, such as microporous thermal and electricalinsulation material. A heating element 49 is provided secured relativeto the base layer 47. As shown, the heating element 49 comprises acorrugated metal ribbon mounted edgewise on the base layer 47 andsecured by partial embedding in the base layer. Such a heating elementis well known to the skilled person. The heating element couldalternatively be of coiled wire or coiled ribbon secured to the baselayer or of lamp form mounted above the base layer, or a sheathedheating element of well known form, or a wire resistance element mountedwithin a glass or quartz tube. Clearly, the internal configuration ofthe dish-like support may require modification depending on the natureof the heating element employed.

A peripheral wall 51 of thermal insulation material is provided in theheater and extends around the internal periphery of the dish-likesupport. As shown, the peripheral wall may be separate from the baselayer 47, but the peripheral wall could alternatively be providedintegral with the base layer, as is well known in the art.

The dish-like support 45 is substantially circular and underlies themajority of the dished member 43, including the area immediately abovethe shaft 41.

The turntable 19 can be removed for cleaning and is interchangeable withalternative turntables (which may or may not be heated) or alternativeheating means.

The heating power output of the auxiliary heater 29 preferably increasesas the distance from the axis of the turntable increases so as toprovide substantially even heating of the food item irrespective of thedistance from the axis of the turntable.

The fan-assisted oven shown in FIGS. 8 and 9 comprises a body having atop 52, a base 53, a back 55, side walls 57 and 59 and a door 61provided with a handle 63 for opening and closing the door. A controlpanel 65 is provided for controlling operation of the oven. Providedwithin an oven cavity 67 is a turntable 19 which is rotatable in knownmanner when the oven is in operation.

A main heating element 71 is provided behind the back 55 of the ovencavity and a fan 73 propels air past the heating element and distributesthe hot air around the oven cavity for relatively even heating of thetop and sides of a food item 75 to be heated. The hot air from the mainheating element 71 is very effective at heating the upper part of a fooditem 75, but is not as effective at heating the lower part of the fooditem.

The upper part of food item 75 may additionally be heated with a grillheater 77 provided in the region of the top 51 of the oven body anddirected downwardly onto the upper part of the food item.

However, while the hot air from main heating element 71 and grill 77 ifenergised effectively heat the upper part of the food item 75, the lowerpart of the food item is not effectively heated and this can lead eitherto the upper part of the food item being over-cooked or the lower partof the food item being under-cooked. Either case is visuallyundesirable, while under-cooking of the lower part of the food item canbe hazardous to health.

As with the microwave oven described hereinabove, an auxiliary heater 29is integrated into the base of the turntable 19. The auxiliary heater 29is as shown in FIGS. 3 to 7 as described in more detail hereinabove.

1. An oven comprising an oven cavity, a main heating means for heating afood item, and a turntable arranged in a lower region of the oven cavityand comprising a surface for heating a food item (27, 75) placed on theturntable (19), wherein the turntable (19) is provided with integralelectrical heating means (29) and with electrically-conductive means forconnecting the integral electrical heating means to a source ofelectrical power.
 2. An oven as claimed in claim 1, wherein the heatingmeans (29) comprises an elongate electrically conducting materialembedded into the turntable.
 3. An oven as claimed in claim 2, whereinthe heating means is embedded into a lower surface of the turntable. 4.An oven as claimed in claim 1, wherein the heating means comprises athick film heating element.
 5. An oven as claimed in claim 4, whereinthe thick film heater is applied to an underside of the turntable.
 6. Anoven as claimed in claim 4, wherein the thick film heater is applied toan upper surface of the turntable.
 7. An oven as claimed in claim 1,wherein the heating means comprises a heating element wrapped around aninsulating board.
 8. An oven as claimed in claim 7, wherein the boardcomprises mica.
 9. An oven as claimed in claim 1, wherein a layer ofthermal insulation material (31) is included on a lower surface of theturntable.
 10. An oven as claimed in claim 1, wherein the heating meanscomprises a heating element (49) provided within a dish-like support(45) containing a base layer (47) of thermal insulation material.
 11. Anoven as claimed in claim 10, wherein the base layer (47) comprisesmicroporous thermal and electrical insulation material.
 12. An oven asclaimed in claim 10, wherein the heating element (49) is supportedrelative to the base layer.
 13. An oven as claimed in claim 12, whereinthe heating element (49) comprises a corrugated metal ribbon mountededgewise on the base layer (47) and secured by partial embedding.
 14. Anoven as claimed in claim 12, wherein the heating element (49) comprisesmeans selected from a coiled wire and a coiled ribbon secured to thebase layer (47).
 15. An oven as claimed in claim 12, wherein the heatingelement (49) comprises a lamp mounted above the base layer (47).
 16. Anoven as claimed in claim 12, wherein the heating element (49) comprisesa sheathed heating element.
 17. An oven as claimed in claim 12, whereinthe heating element (49) comprises a resistance element mounted within aglass tube.
 18. An oven as claimed in claim 10 wherein a peripheral wall(51) of thermal insulation material is included extending around theinternal periphery of the dish-like support (45).
 19. An oven as claimedin claim 1, wherein the heating power output of the heating means (29)increases with increasing distance from an axis of rotation of theturntable.
 20. An oven as claimed in claim 1 wherein conductive tracks(35, 37) connected to the heating means are included for supplying powerto the heating means.
 21. An oven as claimed in claim 20, wherein theconductive tracks (35) are in the form of annular tracks provided on anunderside of the turntable (19).
 22. An oven as claimed in claim 20,wherein the conductive tracks (37) are provided around the periphery ofa support shaft (41) provided on an underside of the turntable (19). 23.(Cancelled)
 24. An oven as claimed in claim 1, wherein the main heatingmeans comprises a magnetron (23).
 25. An oven as claimed in claim,wherein the main heating means comprises a resistance heating element(71) and fan means (73) for propelling air past the heating element (71)and into the oven cavity (67).
 26. An oven as claimed in claim 24,wherein the main heating means further comprises a grill element (77)for directing radiation downwardly towards the food item.
 27. An oven asclaimed in claim 25, wherein the main heating means further comprises agrill element for directing radiation downwardly towards the food item.